1. Field of the Invention
The present invention relates generally to computer security, and more particularly but not exclusively to methods and apparatus for scanning files for malicious codes.
2. Description of the Background Art
Computer viruses, worms, Trojans, rootkits, and spyware are examples of malicious codes that have plagued computer systems throughout the world. Although there are technical differences between each type of malicious code, malicious codes are also collectively referred to herein as “viruses.” Malicious codes have become so prevalent that experienced computer users have some form of antivirus in their computers. Antivirus for scanning computer files for malicious codes is commercially available from several vendors, including Trend Micro, Inc. A typical antivirus includes a scan engine and a pattern containing signatures of malicious codes and other information for identifying malicious codes. Generally speaking, the scan engine scans a target file for malicious codes by comparing the target file's contents against the malicious code signatures in the pattern. The pattern is periodically updated to include new information about known or newly discovered malicious codes. When the pattern is updated, files that have been scanned using a previous pattern may have to be rescanned as they may be infected by viruses that cannot be detected using the previous pattern.